Key features of the case study
As part of the project “De Dommel natuurlijk schoon” the reach Klotputten-Verdeelwerk of the river Dommel within the borders of the city of Eindhoven was restored in 2007 over a length of approximately 0.9 km. To create more habitat heterogeneity, two secondary channels were dug and the streambed was modified, resulting in more gently sloping banks. Other measures were the excavation of pools in the floodplain and the construction of a fishway.
The source of the river Dommel is found south of the village Peer in Belgium, from where its flows over a length of approximately 120 km through the northeastern part of Belgium and the southern part of the Netherlands until it joins the river Meuse. The site of the restoration project in located in the city of Eindhoven and is bordered by a densely populated residential area in the north (Ooievaarsnest and Hanevoet) and the campus of the Eindhoven University of Technology in the south. At this point the river has a total upstream catchment area of about 400 km2. The Dommel is a low gradient (height difference 35 m) slowly flowing lowland river, with a mean annual discharge near the study site of 2.6 m³/s.
Drivers and pressures
The course of the river Dommel in the city of Eindhoven has been strongly modified. Channelization continued until the 1970's, transforming a meandering river into a straightened channel with reinforced banks. Furthermore, the river channel was diverted because of highway construction, weirs were constructed to regulate flow and a large pond (Klotputten) acting as a sand trap was created. As a consequence, natural flow dynamics and with that its associated morphological processes were lost. Another problem was the presence of heavily polluted sediments. In the past the riverbed has been contaminated with cadmium and zinc released by an upstream zinc smelter.
After dredging the contaminated sediments in previous restoration projects, the local water authorities planned to rehabilitate the river within the borders of the city of Eindhoven, aiming at transforming the straightened river channel into a meandering channel and initiate erosion-sedimentation processes to create more natural river banks which allow riparian vegetation development (Waterschap de Dommel, 2007). Erosion and sedimentation processes were allowed up to a point were conflicts might arise with other functions.
The main bed profile was adjusted to create a small summer bed and a wider winter bed and two bended secondary channels were dug (Figure 1), resulting in the formation of two islands in the river. To prevent too much erosion, the banks of the secondary channels were reinforced with small tree trunks. Furthermore, two 500-m2-ponds with a maximum depth of 1.5 m were created in the floodplain, riparian vegetation was planted and a fish ladder was constructed to make the downstream weir passible for migrating fish.
The measures should result in optimal conditions for the following fish species: river- and brook lamprey (Lamptera fluviatilis and L. planeri), stone loach (Barbutula barbutula), common dace (Leuciscus leuciscus), ide (L. idus), chub (Squalius cephalus), bullhead (Cottus sp.), gudgeon (Gobio gobio), spined loach (Cobitis taenia) and burbot (Lota lota), which was defined as a minimum water depth of 30 cm and a maximum (average) current velocity near the river bottom of 0.3-0.4 m/s during the year (Waterschap de Dommel, 2007).
Monitoring before and after implementation of the project
No before and after monitoring data are available from the restored reach, but several points in the river are measured continuously (e.g. discharge, dissolved oxygen availability) monthly (physical-chemical parameters), and once every 1-5 years (macroinvertebrates, fish, macrophytes).
The restored and an upstream degraded control reach were investigated in REFORM (i.e. using a space-for-time substitution approach).
The bed profile is considered too large for the volume of water available to meet the goals set at the start of the project; especially during periods of low discharge current velocity is low (Hermsen & Berg, 2015). Furthermore, substrate heterogeneity is regarded as too low. REFORM-measurements confirmed this observation. The shallow main channel (0.4 m deep) was heavily vegetated and the bed substrate was dominated by silt. The new secondary channel was deeper (1.1 m) and had a lower vegetation coverage in comparison to the main channel, but the substrate was also dominated by silt. To improve instream conditions new measures are prepared (Hermsen & Berg, 2015): (i) stimulating a flow increase in the secondary bend channel by increasing the height of the ford present in the main channel by adding gravel, (ii) adding wood to the river channel to increase habitat heterogeneity.
In 2012 species richness of macroinvertebrates was very similar in the restored reach in comparison to an upstream unrestored reach: 83 species in the restored reach versus 84 in the unrestored reach of which in the restored reach 11 species (252 indivuals) were regarded as WFD-indicator species for the Dutch river type R06 (slow flowing lowland river on sand) and 10 species (259 individuals) in the unrestored reach. Regarding macrophytes, both the restored and the unrestored reaches were dominated by Sparganium.
The river itself and the adjacent area are used intensively for recreational purposes (hiking, walking dogs, fishing, canoeing), especially by the inhabitants of the residential areas bordering the river to the north. During the planning stage of the project attention has been paid to retaining the recreational value of the rehabilitated area after the measures have been taken, for example, by creating a new hiking path and a facilities for canoeing.
Contact person within the organization
Waterschap De Dommel Postbus 10.001 5280 DA Boxtel Tel. +31411 618 618
Extra background information
Hermsen, F., Berg, M. (2015). Projectplan herinrichtingsmaatregelen Dommel t.h.v. de Klotputten. Waterschap de Dommel, Boxtel.
Waterschap De Dommel (2007). Herinrichting Dommel Aanleg meanders traject Klotputten – verdeelwerk. Waterschap de Dommel, Boxtel.
- Remeander water courses
- Install fish pass/bypass/side channel for upstream migration
- Create low flow channels in over-sized channels
- Remove bank fixation
- Revegetate riparian zones
- Remove bank fixation
- Construct semi-natural/articificial wetlands or aquatic habitats